1. Field of the Invention
The present invention relates to a waveguide-tube structure (waveguide structure) suitable for transmission of a microwave or a millimeter wave.
2. Description of the Related Art
FIG. 10 is a cross-sectional view illustrating an example of prior art waveguide tube (waveguide structure).
For example, the waveguide tube is configured in such a way that two approximately rectangular-parallelepiped conductive members 10 and 20 are laminated, and grooves 10a and 20a formed in the respective surfaces of the conductive members 10 and 20 are made to face each other; as a result, a hollow waveguide tube 30 having an approximately rectangular cross section.
In addition, the waveguide tube 30 is formed in a linear shape, and the direction of the tube axis thereof is perpendicular to the paper plane of FIG. 10.
The plane on which the conductive members 10 and 20 face each other is the division plane of the waveguide tube 30.
The hollow waveguide tube 30, of this kind, that is divided by a division plane and whose cross section has a rectangular shape can be manufactured through die-casting, whereby the production costs can be suppressed to be relatively low.
Methods of dividing the waveguide tube 30 include a method of dividing a waveguide tube by a division plane parallel to the transverse side of a cross section of the waveguide tube and a method of dividing a waveguide tube by a division plane parallel to the longitudinal side of a cross section of the waveguide tube.
In the case where a waveguide tube is formed through a division structure, deterioration of the transmission performance can be suppressed more effectively by utilizing the method of dividing the waveguide tube by a division plane parallel to the transverse side of a cross section of the waveguide tube, as illustrated in FIG. 10.
However, in the case where the longitudinal side of a waveguide tube is divided by a division plane parallel to the transverse side of a rectangular cross section of the waveguide tube, the groove depth is longer than the groove width, whereby the manufacturing through molding is liable to become difficult.
In the case of die-casting or the like, in general, the longer than the groove width the groove depth is, the more difficult it is that the melted metal flows into the front end of the wall that forms the groove; therefore, there has been a problem that the molding accuracy is deteriorated.
Moreover, there has been a problem that, the longer the groove depth as compared to the groove width, the shorter the lifetime of a die that is utilized for die-casting. Also, the production costs eventually become expensive.
In Japanese Patent Application Laid-Open No. 2004-48486 (Patent Document 1), there is disclosed “a waveguide tube characterized by having a structure in which two tub-shaped divided members obtained through division by an H-plane or an E-plane are bonded to each other, and characterized in that the cross section thereof perpendicular to the longitudinal direction thereof has a hexagonal shape”.
The structure of the waveguide tube disclosed in Patent Document 1 is similar to the structure of the waveguide tube illustrated in FIG. 10 “in terms of the fact that a hollow waveguide tube is formed of two divided members (i.e., two tube-shaped divided members)”.
As measures for the foregoing problems in the known waveguide tube, there is conceivable a method in which a waveguide tube is formed by applying metal plating to a resin member or the like that has a superior moldability.
However, in some cases, due to a structural factor, the need for heat radiation, or the like, resin cannot be utilized for both of the conductive members 10 and 20 that configure the waveguide tube 30; thus, the waveguide tube 30 cannot help being formed by utilizing metal only for one of the conductive members 10 and 20 and combining the metal member and the resin member.
In this case, due to contact friction caused by the linear-expansion difference between the members, separation of metal plating occurs in a junction surface produced by laminating the metal member 10 and the resin member 20 to which metal plating is applied.
When separation of metal plating occurs, separation powder of the metal plating becomes floating dirt in the waveguide tube, thereby deteriorating the transmission performance, or a separation portion produced by friction causes a separation area to expand; thus, there eventually occurs a problem, such as the occurrence of wall-face separation of the waveguide tube, which considerably deteriorates the function of the waveguide tube.
Moreover, there occurs a problem that, due to the linear-expansion difference between the laminated members (i.e., the laminated metal member 10 and resin member 20), “the relative position between the laminated members is displaced”.
It goes without saying that, when the relative position between the laminated members (i.e., the laminated metal member 10 and resin member 20) is displaced, the transmission performance (propagation performance) is affected.
Here, the reason why separation of metal plating occurs in the known waveguide tube will be explained in detail.
As illustrated in FIG. 10, the hollow waveguide tube 30 is configured by laminating the members 10 and 20 in such a way that the linear grooves 10a and 20a that are formed in the respective surfaces of the members 10 and 20 face each other.
With the configuration of the waveguide tube illustrated in FIG. 10, in the case where the waveguide tube 30 is formed by laminating the members 10 and 20 that are made of different materials, due to the linear-expansion difference between the members, contact friction occurs at a position where the members make contact with each other.
With such a waveguide tube configuration as illustrated in FIG. 10, because the metal member 10 and the resin member 20 to the surface of which metal plating is applied directly make contact with each other, change in the temperature under the environment of actual use causes contact friction produced by the linear-expansion difference between the members to occur at a position where the members make contact with each other; therefore, there exists a problem that the metal plating applied to the surface of the resin member 20 is separated and separation powder is produced.
In FIG. 10, the member 10 is formed of a metal material such as SUS (stainless steel) or AL (aluminum); the member 20 is formed of a material obtained by applying plating of metal such as nickel to the surface of a resin material such as ABS (acrylonitrile butadiene styrene) or PEI (polyetherimide).
As described above, in the waveguide tube 30 in which the members 10 and 20 that are made of different materials are laminated, due to the difference between the linear-expansion coefficients of the members 10 and 20, the expansion/contraction amounts of the members differ from each other, when the environmental temperature changes.
For example, in the case where the member 10 is formed of SUS having a linear-expansion coefficient of 1.7×10−5, and the member 20 is formed of ABS having a linear-expansion coefficient of 8.5×10−5, 50-degree change in the temperature causes the expansion/contraction amounts per 50-millimeter basic line to differ by 0.17 mm from each other, whereby the difference in the deformation amount causes friction.
The contact friction causes separation of metal plating in a known waveguide tube.
In the case where, as illustrated in FIG. 10, the waveguide tube is divided at the middle of the longitudinal side thereof (i.e., the depths of the grooves 10a and 20a are equal to each other), the groove depths are longer than the respective groove widths, whereby the molding of the metal members through die-casting may become difficult.
Accordingly, the yield rate of the product is deteriorated, and the lifetime of the die is shortened.
In order to cope with this problem, it is desired to make the depth of the groove formed in the surface portion of the metal member shorter than the depth of the groove formed in the surface portion of the resin member.